In order to minimize the space required by display devices, research into the development of various flat panel display devices such as LCD display devices, plasma display panels (PDP) and electro-luminescence displays (EL) has been undertaken to displace larger cathode-ray tube displays (CRT) as the most commonly used display devices. Particularly, in the case of LCD display devices, liquid crystal technology has been explored because the optical characteristics of liquid crystal material can be controlled in response to changes in electric fields applied thereto. As will be understood by those skilled in the art, a thin film transistor liquid crystal display (TFT LCD) typically uses a thin film transistor as a switching device and the electrical-optical effect of liquid crystal molecules to display data visually.
At present, the dominant methods for fabricating liquid crystal display devices and panels are typically methods based on amorphous silicon (a-Si) thin film transistor technologies. Using these technologies, high quality image displays of substantial size can be fabricated using low temperature processes. As will be understood by those skilled in the art, conventional LCD devices typically include a transparent (e.g., glass) substrate with an array of thin film transistors thereon, pixel electrodes, orthogonal gate and data lines, a color filter substrate and liquid crystal material between the transparent substrate and color filter substrate. The use of a-Si TFT technology typically also requires the use of separate peripheral integrated circuitry to drive the gates and sources (i.e., data inputs) of the TFTs in the array. In particular, gate driving signals from a gate driving integrated circuit are typically transmitted to the gate electrodes of TFTs in respective rows and data driving signals from a data driving integrated circuit are typically transmitted to the source electrodes of TFTs in respective columns. A display is typically composed of a TFT substrate in which a plurality of liquid crystal pixels are formed. Each pixel typically has at least one TFT and a pixel electrode coupled to the drain of the respective TFT. Accordingly, the application of a gate driving signal to the gate of a TFT will electrically connect the pixel electrode of a respective TFT to the data line connected thereto.
Referring now to FIG. 1, a first TFT LCD display cell of a conventional TFT LCD display device is illustrated. Each cell comprises a TFT transistor having a source electrode connected to a data line (DL), a gate electrode connected to a gate line (GL) and a drain electrode connected to a respective pixel electrode internal to the cell. As will be understood by those skilled in the art, a storage capacitor (Cst) is utilized to sustain the pixel electrode voltage during holding periods and the liquid crystal capacitor (C.sub.LC) is connected in series between a respective pixel electrode and a common electrode (Vcom) of a color filter substrate. The storage capacitor also has an electrode connected to a storage electrode line (SL). The storage capacitors of adjacent display cells in a row thereof may also have electrodes which are connected to the storage electrode line (SL). However, as will be understood by those skilled in the art, the use of an independent storage electrode line (SL) for each row of display cells may decrease the display device's aperture ratio.
Referring now to FIG. 2, another conventional TFT LCD display device is illustrated. Each cell comprises a TFT transistor having a source electrode connected to a data line (DL), a gate electrode connected to a gate line (GL) and a drain electrode connected to a respective pixel electrode internal to the cell. As illustrated, a liquid crystal capacitor (C.sub.LC) in each cell is connected in series between a respective pixel electrode and a common reference potential (Vcom) and the storage capacitor in each cell is connected in series between a respective pixel electrode and a next lower order gate line (GL). Unfortunately, although the aperture ratio of the device of FIG. 2 may be greater than the aperture ratio of the device of FIG. 1, the parasitic capacitance of each gate line (GL) is relatively high in the device of FIG. 2. Moreover, in the event any of the TFTs in the devices of FIGS. 1 and 2 are defective, the voltage on the corresponding pixel electrode may be driven to a level which is significantly different than the value of the data to be loaded into the defective cell and this can corrupt the fidelity of the final displayed image.
Accordingly, notwithstanding the above described display devices, there still continues to be a need for improved display devices which have high aperture ratio and reduced parasitic gate line capacitance.